The novel regeneration scheme disclosed herein is employed in ethylene-higher alpha olefin copolymerizations. Typically, the alpha olefin will have the general formula: R -- CH = CH.sub.2, where R is a C.sub.1 to C.sub.8 alkyl radical, preferably a C.sub.1 to C.sub.4 alkyl radical. The alpha olefin may be linear or branched and, while a single alpha olefin is preferred, mixtures may be employed. Illustrative examples include propylene; 1-butene; 1-heptene; 1-decene; 4-methyl-1-pentene; 4,4'-dimethyl-1-hexene; 5,6,6-trimethyl-1heptene, etc.; particularly preferred herein is propylene.
The copolymers may be a terpolymer wherein the third monomer is a nonconjugated diene preferably having 6 to 15 carbon atoms. These types of terpolymers are known as ethylene-propylene-diene terpolymers, i.e., EPDMs. Representative useful dienes include 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 5vinyl-2-norbornene, 2-ethyl-norbornadiene, 1,4-hexadiene, dicyclopentadiene, 4,7,8,9-tetrahydroindene, etc. Preferred herein is 5-ethylidene-2-norbornene.
The monomeric reactants are typically present in the following amounts, measured per 100 parts of polymerization solvent: about 0.1 to about 10.0, preferably 1.0-6.0 (e.g., 2.75) parts ethylene; about 0.1 to about 20.0, preferably 1.0-15.0 (e.g., 12.5) parts alpha olefin (e.g., propylene); from 0.0 to about 2.0, preferably 0.0-1.0 (e.g., 0.22), parts diene (e.g., 5-ethylidene-2-norbornene). Here, as elsewhere in this specification, all parts given are parts by weight unless otherwise specifically stated.
The catalyst composition preferably employed in making these polymers is a Ziegler-type catalyst and may include a compound of a transition metal (preferably a halide such as titanium tetrachloride or vanadium tetrachloride) together with, as cocatalyst, an organometal compound (e.g., an organoaluminum compound such as diethylaluminum chloride). The mole ratio of cocatalyst to catalyst is generally in the range of 1:1 to 16:1, preferably 1.5:1 to 7:1. The total catalyst composition used in polymerization may vary depending upon the particular components used, but is generally in the range of about 0.01 to about 0.1 parts, preferably 0.05 parts, per 100 parts of diluent.
The polymerization diluent is a nonreactive medium, typically an aromatic hydrocarbon such as toluene, a saturated aliphatic hydrocarbon such as heptane, pentane or hexane, or a chlorohydrocarbon such as tetrachloroethylene. Hexane is preferred.
Reaction temperatures for polymerization are in the range of about 10.degree. to about 75.degree.C., preferably about 25.degree. to about 40.degree.C. (e.g., 30.degree.C.). Reactor pressures should be above the vapor pressure of the reacting medium at reactor temperature. Normally pressures are in the range of about 0 to about 70 atmospheres, preferably about 4 to about 10 atmospheres (e.g., 6 atm.). All steps in the reaction should be carried out in the absence of oxygen, moisture, CO.sub.2 or other harmful materials. Therefore, all components of the reaction mixture should be pure and dry and blanketed with inert gas such as nitrogen or methane.
After reaction, the reactor effluent, as withdrawn, normally contains unreacted light monomer (e.g., ethylene and propylene), unreacted termonomer when employed, and copolymer, this being dissolved in diluent to form a solution containing about 3 to about 15, typically 5 parts copolymer per 100 parts diluent, i.e., polymer cement. This effluent is withdrawn at a temperature of about -10.degree.C. to about 70.degree.C., typically 30.degree.C., and a pressure of about 4 to about 10 atmospheres, typically 6 atmospheres.
The reactor effluent is then subjected to flashing at reduced pressures in order to separate as overhead substantially all unreacted ethylene. Flashing conditions are in the range of about 10.degree. to about 50.degree.C., typically 20.degree.C., and about 1.0 to about 2.0 atmospheres, typically 1.2 atmospheres. Under these conditions some unreacted higher alpha olefin (e.g., propylene) and some diluent may also be withdrawn as overhead. This overhead may be directly recycled.
The flash bottoms, containing polymer cement, diluent, unreacted higher alpha olefin, some active and some spent catalyst is then subjected to catalyst quench and deashing (i.e., catalyst residue removal) by contact with water which may contain small amounts of alcohols such as methanol and/or acids such as sulfuric or hydrochloric acid as deashing aids.
After deashing the polymer effluent is subjected to steam stripping to remove as overhead substantially all diluent, steam, substantially all remaining higher alpha olefin and unreacted diene if employed; and, as bottoms, a copolymer slurry in water. This stripping operation is conducted at a temperature in the range of about 60.degree. to about 130.degree.C., typically 110.degree.C., and a pressure of from about 0.5 to about 3 atmospheres, typically 2 atmospheres.
The overhead is fractionated in vaporous form to remove heavy impurities from the polymerization diluent and is then subjected to partial condensation at a temperature of about 20.degree. to about 50.degree. C., typically 30.degree. C., and a pressure of about 1.0 to about 2.0 atmospheres, typically 1.4 atmospheres, in order to condense and liquefy substantially all diluent (e.g., hexane) and steam. Under these partial condensation conditions the higher alpha olefin remains gaseous and is readily separated from the condensed components. However, significant amounts of water vapor may also remain uncondensed; therefore the alpha olefin must be dried prior to recycle to the polymerization reactors. For this purpose driers containing adsorbent materials such as activated alumina are preferred. After a time such materials will, of course, become saturated and must be replaced or regenerated.